<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <script>
    function getnum(arr = []) {
      let max = arr[0]
      let min = arr[0]
      for (let i = 0; i < arr.length; i++) {
        if (max < arr[i]) {
          max = arr[i]
        }
        if (min > arr[i]) {
          min = arr[i]
        }
      }
      return [max, min]
    }
    let result = getnum([1, 2, 3, 4, 5, 6, 7, 8, 9])
    console.log(result)
  </script>
</body>

</html>